Defrosting means for refrigerating systems



Oct. 19, 1954 V. W. SMITH DEFROSTING MEANS FOR REFRIGERATING SYSTEMS Filed Sept. 16, 1950 g 2 g l A B NORMAL CLOCK NORMAL REFRIG. CYCLE DEFROST CYCLE REFRIGCYCLE 46 I l l c\, 44 I I l I Q I 40 I D l y I l V i2 E F I 2a E E INVENTOR.

VICTOR 14 SM/TH Patented Oct. 19, 1954 i fi'i' NT OFFICE DEFROSTING MEANS FOR REFRIGERATING SYSTEMS Victor W. Smith, Trenton, N. 1., assignor to C. V.

Hill & Company, Inc., Trenton, N. 1., a corporation of New Jersey 6 Claims.

This invention relates to means for controlling the operation of refrigerating systems and is directed particularly to systems including control means which prevent excessive ris in tempera ture during a defrosting cycle.

The problem of regulating the temperature of a refrigerated space during a defrosting operaion has always been troublesome. This is particularly true when the refrigerated space is to be maintained at a temperature below freezing since any material rise in temperature may result in loss or deterioration of the products being refrigerated.

It has been common practice heretofore to provide time controlled means for initiating and terminating the defrosting cycle, but the duration and frequency of the cycle required for different types of equipment varies greatly. Moreover, the amount of frost which accumulates on an evaporator during any refrigerating cycle depends upon many fluctuating factors such as the humidity of the air, the manner in which the equipment is used and other conditions which change from day to day and even from hour to hour. Therefore a time cycle which is adequatefor one set of conditions may be insufficient to clear the frost from the evaporator under other conditions. As a result, frost may build up on one occasion to such an extent as to render the equipment inefficient if not actually inoperative, whereas on other occasions when using the same period for defrosting, the ice may be melted quickly and the temperature of the refrigerated space will thereafter continue to rise so that excessive variations in temperature take place.

In other systems the defrosting cycle is initiated and terminated in response toa rise in pressure of the refrigerant in the evaporator or on the intake side of the compressor. In the patent to MacMaster No. 2,494,480 filed April 29, 1946, the defrosting cycle is initiated by time controlled means and terminated by pressure controlled means. Other variations in operation of the control means for defrosting equipment are known but the different conditions under which refrigerating equipment operate gives rise to such variations in performance that undesired fluctuations in temperature of the refrigerated space frequently occur.

In accordance with the present invention these objections to prior control systems are overcome by providing a combination of control means which prevent excessive rise in temperature of the fixtureduring the defrosting cycle. This is accomplished by employing controls which permit limited operation of the refrigerating means during the defrosting cycle and to the extent necessary toprevent undue rise in temperature. Thus the temperature of the evaporatormay be raised sufliciently to melt-the ice and froston the evaporator, say to a temperature between 34 and 38 F., but further rise in temperature is prevented by intermittent operation on a refrigerating cycle. Melting of frost can then continue'throughout a prolonged-clefrosting period but the temperature of the evaporator and of the refrigerated space will not fluctuate excessively and the normal refrigerating temperature will be restoredpromptly after the normal refrigerating cycle is renewed.

One of the objects of the present invention is to provide a novel type of control means for defrosting equipment'of refrigerating systems.

A particular object of the invention is to prevent excessiverise in temperature of refrigerating means during a defrosting cycle.

A specific object of the invention is to provide control means for refrigerating systems wherein the duration of adefrosting cycle is established by time controlledmeans but sufficient refrigeration is provided during such period to prevent excessive risein temperature of the evaporator and of the air in the refrigerated space during the defrosting cycle.

These and other objects and features of the present invention will appear from the following description thereof in which a typical embodiment .of theinvention is referred to for the purpose of indicating the nature of the invention but withoutintending to limit the scope of the invention thereby.

In the drawing:

Fig. 1 is a diagrammatic illustration of one type of refrigerating system and control means embodying the present invention; and

Fig. 2 is a typicalchart showing variations in temperature of equipment embodying the present invention.

The control means of the present inventioncan be applied tosu'bstantiallyany form of refrigerating system employing a compressor, condenser and evaporator, but for purposes of illustration, a system of the simplest conventional type is shown. Thus the system illustrated comprises a compressor 2 driven by a motor '4, a condenser 6, a receiver 8 and an evaporator It. .Hot refrigerant gas from the compressor ispassed to the condenser 6 during the normal refrigerating operation through the high pressure'line l 2. The condensed refrigerant passes to the receiver 8 and flows to the evaporator .Hl through refrigerant line Hi and expansion valve it. The expanded and cooled refrigerant gas returns from the evaporator through the low pressure line 58, a reheater 2i) and return line 22 to the intake side of the compressor 2. I

The duration of the refrigerating and defrosting cycles is controlled by a time clock 24 which operates to terminate the refrigerating Cycle and initiate a defrosting cycle on closing an electrical contact such as the contact 25. When this contact is closed, solenoid 28 is energized by the flow of current from the positive side 30 of a power line through the conductor 32 and normally closed contact 34 to contact 25. Current returns from the solenoid 28 through conductor 36 to the negative side 38 of the power line. When the solenoid 28 is energized it serves to open a valve 40 in by-pass line 42. The by-pass line extends from high pressure line IE to a point adjacent the evaporator Hl so as to by-pass the condenser 6, receiver 8 and expansion valve I6. Hot gas from the compressor then flows to the evaporator l and melts the ice and frost on the coils, fins, drip pans and other surfaces associated with the evaporator. In melting the ice and frost a substantial part of the refrigerant gas is condensed so that it returns through the low pressure line I8 as a liquid. Before reaching the reheater 2B, the refrigerant flows through a constant pressure valve 44 which serves to maintain the gas returning to the compressor through return line 22 at a relatively low and constant pressure. At the same time, moisture containing air is circulated over the coils of the reheater by a. blower 46 to give up latent and sensible heat to the reheater for revaporizing the refrigerant. The expansion of the liquid refrigerant entering the reheater and the absorption of heat thereby serves to insure the revaporization of all of the refrigerant prior to its return to the intake side of compressor 2.

The defrosting cycle is initiated and terminated by the time clock and will continue for the full period for which the time clock has been set to operate. However, in accordance with the present invention, supplemental control means are provided to renew the refrigerating operation temporarily during the defrosting cycle when the temperature of the evaporator rises above a predetermined maximum. Such control means are preferably actuated in response to a rise in the pressure of the refrigerant gas returning to the compressor through low pressure line l8. This pressure will rise when ice or frost has been cleared from the evaporator and little or no refrigerant is condensed by its passage through the evaporator. If the pressure rises sufficiently prior to the end of the defrosting period as established by the time clock, say to a pressure corresponding to a temperature of 36 or 38 F., a pressure responsive device 48 operates to move the normally closed contact as to an open position shown in dotted lines in Fig. 1 to break the solenoid circuit. The valve M1 in by-pass line 42 is then actuated to terminate the flow of hot refrigerant gas to the evaporator and permits the flow of liquid refrigerant to the evaporator through expansion valve 16.

When the refrigerating operation is thus renewed it serves to check the rise in temperature of the evaporator and instead the temperature of the evaporator and the pressure of the returning refrigerant gas in low pressure line I 8 willfall until the pressure responsive device 48 operates to close contact 34 again. The normal defrost-' ing operation is thereafter continued until the pressure in the low pressure line l8 again rises unduly high. In this way temporary and intermittent refrigeration is caused to take place during the defrosting period to the extent necessary to prevent a rise, in temperature substantially above that required to insure'defrosting of the evaporator. 1 i

The expansion device 38 is of course normally contracted and contact 34 continually remains closed during the refrigerating cycle since the pressure of refrigerant gas in low pressure line I8 is maintained relatively low during such operation. Similarly the expansion device is contracted and contact 34 remains closed during the defrosting cycle unless the pressure in line it rises in response to a rise in temperature of the evaporator and returning refrigerant gas.

In a typical operation pressure responsive device lS is adjusted to expand and break the solenoid circuit when the temperature of the evaporator reaches 36 or 38 F. and is adjusted to contract so as to close contact 33 and complete the solenoid circuit when the temperature of the evaporator falls below 34 F. Adjustment of the temperature responsive device to actuate the normally closed contact 34 may be effected by any suitable means, such as the threaded end member 59, which may be turned in or out until it is spaced a desired distance from the contact member 34. and contraction of the temperature responsive device $8, the contact 34%, will be opened and closed at predetermined pressures corresponding to desired limiting defrosting temperatures. The pressure responsive device therefore serves as a defrost limit switch or variable temperature 11m iting means which causes the refrigerating cycle to be renewed temporarily and as often as may be required to prevent the temperature of the evaporator and of the air in the refrigerated space from rising appreciably above freezing or such other predetermined maximum for which it may be adjusted. A limiting minimum defrosting temperature is also established to insure continued defrosting of the evaporator by closing the contact 34 while the evaporator temperature and pressure are still high enough to continue their intended defrosting action. The rise and fall in temperature during a defrosting cycle is thus limited so as to preclude undesired fluctuations in temperature of the refrigerated equip ment at any time during the defrosting cycle.

Fig. 2 shows a typical temperature curve obtained when employing the control means of the present invention. It includes the first stage A corresponding to final period of a normal refrigerating cycle in which the temperature varies from say 28 to 32. When the time clock operates at the time B, it initiates a defrosting cycle and the temperature of the evaporator rises to say 38. In the absence of the present invention the temperature of the evaporator would continue to rise as represented by the broken line C until the conclusion of the refrosting period as determined by the setting of the time clock. However, by providing the temperature limiting means of the present invention, the refrigerating cycle will be temporarily renewed when the temperature reaches the predetrmined maximum of 38 F., or other temperature indicated at D for which the defrost limiting device has been adjusted. The temperature then falls until it reaches a predetermined minimum say 34 F. as indicated at E whereupon the defrosting operation is resumed.

Thereafter upon expansion The temperature thus will be maintained within the range of, say 34 to 38 F. throughout the defrosting period. At the conclusion of the defrosting period as determined by the time clock and indicated at F the contact 2% is opened to break the solenoid circuit for the duration of the refrigerating cycle. The temperature then returns to 28 F. as indicated at the point G and will thereafter vary from 28 to 32 F. under the control of conventional means such as a thermostat (not shown).

The temperature range permitted by the defrost limit control may of course be varied as required in any installation.

The present invention is also adapted for use in systems which already are provided with a time clock controlling the duration of the defrosting period and in such. installations it is only necessary to install the pressure responsive device 58 and its associated circuit control means or othertemperature limiting means for initia ing and terminating the refrigerating operation during the defrosting cycle established by the time clock. On the other hand in new installations, the time clock and the defrost temperature limiting device may be installed as a unit to afford the desired limiting temperature rise during the defrosting cycle.

It will also be understood that the temperature limiting means may be made to respond to conditions other than the pressure of the refrigerant gas returning to the compressor and thus the device indicated at 48 may be a thermostat located at a suitable point or responsive to a predetermined temperature such as the temperature of the evaporator surfaces or the temperature of a refrigerated space. Injury to refrigerated articles can thus be prevented by renewing the refrigerating operation during the defrosting cycle due to emergency or other conditions which may arise and for which no provision has been made heretofore.

While the present invention has been shown I and described with particular reference to those systems wherein the defrosting of the evaporator is affected by means of hot gas passed from the compressor to the evaporator, it will be apparent that the same or similar temperature limiting means may be used in systems wherein defrosting of the evaporator is affected by the absorption of heat from the air adjacent to the evaporator or by any other defrosting means. In view thereof it should be understood that the particular embodiment of the present invention shown in the drawings and described above is intended to be illustrative only and is not intended to limit the scope thereof.

I claim:

1. In a refrigerating system including an evaporator, means for passing refrigerant through said evaporator, defrosting means for raising the temperature of the evaporator to remove ice and frost therefrom, an electrical circuit controlling said defrosting means, a time clock included in said circuit and operable to make and break said circuit at predetermined times to render the refrigerating means inoperative and to establish a defrosting cycle of predetermined duration, and means intermittently operable in response to the temperature of the evaporator to terminate operation of said defrosting means and simultaneously initiate operation of the refrigerating means temporarily during said established defrosting cycle and likewise operable intermittently to restore operation of said defrosting means and simultaneously terminate operation of the refrigerating means temporarily during said established defrosting cycle.

2. In a refrigerating system including a compressor, a condenser and an evaporator, by-pass means for directing hot refrigerant gas from the compressor to the evaporator so as to by-pass the condenser and raise the temperature of the evaporator above freezing to defrost the evaporator, time controlled means connected to the by-pass means and operable at predetermined times to render said by-pass means active and inactive .and thereby establish a defrosting cycle of predetermined duration, and other means controlling operation of said by-pass means to actuate the by-pass means and discontinue flow of hot refrigerant gas to the evaporator and renew flow of refrigerant from the condenser to the evaporator temporarily during the defrosting cycles in response to fluctuations in temperature of the evaporator.

3. In a refrigerating system including a compressor, a condenser and an evaporator, by-pass means for directing hot refrigerant gas from the compressor to the evaporator so as to by-pass the condenser and raise the temperature of the evaporator above freezing to defrost the evaporator, time controlled means connected to the by-pass means and operable at predetermined times to render said by-pass means active and inactive and thereby establish a defrosting cycle of predetermined duration and means responsive to the pressure of refrigerant in the evaporator during said established defrosting cycle and operable to render said by-pass means inactive during the defrosting cycle when said pressure rises to a predetermined point and to render said by-pass means active again when during the defrosting cycle said pressure falls to a predetermined point.

4. In a refrigerating system including a compressor, a condenser and an evaporator, by-pass means for directing hot refrigerant gas from the compressor to the evaporator so as to by-pass the condenser and raise the temperature of the evaporator above freezing to defrost the evaporator, time controlled means connected to the by-pass means and operable at predetermined times to render said by-pass means active and inactive and thereby establish a defrosting cycle of predetermined duration, and means responsive to variations in temperature of the evaporator during said established defrosting cycle and operable to render said by-pass means inactive when the temperature of the evaporator rises to a predetermined maximum and torender said defrosting means active when the temperature of the evaporator falls to a predetermined minimum.

5. A refrigerating system including a compressor, a condenser, an expansion valve, and an evaporator, a by-pass line extending from the compressor to the evaporator so as to by-pass the condenser and expansion valve, a control valve in said by-pass line movable to an open position to allow hot refrigerant gas to flow from the compressor to the evaporator for raising the temperature of the evaporator to effect defrosting thereof and movable to a closed position to cause refrigerant to flow through the condenser,

expansion valve, and evaporator in a refrigerating cycle, an electrical circuit including means for actuating said control valve to move it to said opened and closed positions, time controlled means included in said circuit and operable to make and break said circuit and actuate said valve at predetermined times to establish a defrosting cycle of predetermined duration, and temperature limiting means responsive to variation in temperature of the evaporator and movable to make and break said circuit and actuate said control valve during the defrosting cycle so as to limit the rise in temperature of the evaporator during the defrosting cycle.

6. A refrigerating system including a compressor, a condenser, an expansion valve, and an evaporator, a by-pass line extending from the compressor to the evaporator so as to by-pass the condenser and expansion valve, a control valve in said by-pass line movable to an open position to allow hot refrigerant gas to flow from the compressor to the evaporator for raising the temperature of the evaporator to effect defrosting thereof and movable to a closed position to cause refrigerant to flow through the condenser, expansion valve, and evaporator in a refrigerating cycle, an electrical circuit including means for actuating said control valve to move it to said opened and closed positions, time controlled means included in said circuit and operable to make and break said circuit and actuate said valve at predetermined times to establish a defrosting cycleof predetermined duration, and

temperature limiting means responsive to variation in temperature of the evaporator and movable to make and break said circuit and actuate said control valve during the defrosting cycle so as to limit the rise in temperature of the evaporator during the defrosting cycle, said temperature limiting means being adjustable to actuate said control valve at maximum and minimum temperatures of about 38 F. and 34 F. whereby the evaporator will continue to defrost while undergoing limited rise in temperature during the defrosting cycle established by said time controlled means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,178,445 Warneke Oct. 31, 1939 2,366,635 McCloy Jan. 2, 1945 2,451,682 Lund Oct. 19, 1948 2,481,469 Brown 1. Sept. 6, 1949 2,494,480 McMaster Jan. 10, 1950 2,500,298 Smith Mar. 14, 1950 2,522,199 Shreve Sept. 12, 1950 2,524,568 Kritzer Oct. 3, 1950 2,530,440 Nussbaum Nov. 21, 1950 

